Function Block; Functionality; Operation Principle - ABB RELION 620 Series Technical Manual

Hide thumbs Also See for RELION 620 Series:

Table of Contents

Protection functions

Function block

GUID-2B005C29-6D03-41EF-8CA8-FC4E8D5BB3FB V2 EN

Function block

The transformer differential protection 87T provides up to three three-phase current sets

or restraints designed for protection of two-winding or three-winding transformers and

generator-transformer blocks with a possibility to have two three-phase current sets either

on the winding 1 or winding 2 side in case of two-winding transformer protection. The

function includes a biased low stage and an instantaneous high stage.

The biased low stage provides a fast clearance of faults while remaining stable with high

currents passing through the protected zone increasing errors on current measuring. The

second harmonic restraint, together with waveform-based algorithms, ensures that the low

stage does not trip due to the transformer inrush currents. The fifth harmonic restraint

ensures that the low stage does not trip on apparent differential current caused by a

harmless transformer overexcitation.

The instantaneous high stage provides a very fast clearance of severe faults with a high

differential current regardless of their harmonics.

The setting characteristic can be set more sensitive with tap changer position

compensation. The correction of transformation ratio due to changes in tap position is

done automatically based on the tap changer status information provided to the function

through input.

The function can be enabled and disabled with the Operation setting. The corresponding

parameter values are "Enable" and "Disable".

The operation of transformer differential protection can be described with a module

diagram. All the modules in the diagram are explained in the next sections.

1MAC504801-IB E

620 series ANSI

Technical Manual

Table of Contents